The present invention relates generally to RF rotary joints, or microwave rotary joints, and more particularly to an apparatus having a plurality of conductive fiber brush bundles and a coaxial conductor to transfer RF signal(s) between relatively rotatable objects.
Rotary joints are used to change the direction of microwave propagation between two guides by rotating one with respect to other. RF rotary joints are electromechanical devices that consist of rotational (rotors) and stationary (stators) members. They allow the transmission of RF\microwave signals and power from their rotors to stators or vise verse.
A conventional RF rotary joints consists of either a contacting or non-contacting interface to transfer RF\microwave signals and power.
In non-contacting rotating interfaces, electrical continuity for RF is typically achieved by using λ/4 chokes, to correspond to the quarter wavelength of a particular frequency which eliminate the need for physical contact at the rotating junction. The advantage of a non-contacting interface is that all physical wear is eliminated. Disadvantages of this approach are size and weight, particularly at lower frequencies, which have longer wavelengths and therefore require longer chokes.
In contacting rotating interfaces, two relative rotatable conductive parts keep sliding contact by spring, or other actuators. The advantage of a contacting rotating interfaces is that size can be greatly reduced when compared to a ¼ wavelength choke interface. Disadvantages of contacting rotating interfaces are increased torque, the need for a tight and perfectly concentric fit of the rotating interface, and the fact that contact stress in rotation causes wear and the wear debris would cause electrical failure at the rotating interface. Please see the prior arts: U.S. Pat. No. 3,229,234 A and US2005\0264377A1.
Fiber brush technology has been successfully used in electrical slip ring industry, where, a brush assembly comprising a multifilament conductive fiber brush contacts with a conductive slip ring surface. The brush assembly is constructed with thousands of hair-fine silver alloy fibers running on their tips, offer significant improvement over carbon brushes in both data and current transfer, offering extended brush and slip ring service life, high current capacity, and significant decreases in service acoustic and electrical noise. Please see U.S. Pat. No. 4,398,113 A.